1. Field of the Invention
The present invention relates to an aqueous dispersion for chemical mechanical polishing and a chemical mechanical polishing process making use of this dispersion. Further, the present invention relates particularly to an aqueous dispersion for chemical mechanical polishing that has high shelf stability, prevents deterioration with time even in storage in a state of a high concentration, can provide a polished surface having excellent planarization and lessened surface defects by chemical mechanical polishing and is useful in production of semiconductor devices, a chemical mechanical polishing process excellent in polishing and removal selectivity making use of such a dispersion, and a production process of semiconductor devices.
2. Description of the Background Art
With the increase of the degree of integration and the formation of multi-layer wiring in semiconductor devices, a technique of chemical mechanical polishing is adopted for polishing of a film to be processed. This technique serves to remove an excess wiring material and form a wiring by embedding a proper wiring material in grooves, holes or the like of a desired pattern formed in a dielectrics on a process wafer and then chemically and mechanically polishing the dielectrics.
Such a chemical mechanical polishing process is also applied to formation of capacitors, gate electrodes and the like in addition to the formation of wiring and utilized in specular polishing of a silicon wafer such as an SOI (silicon on insulator) substrate.
Objects to be polished by such a chemical mechanical polishing process include various films such as polysilicon films (polycrystalline silicon films), monocrystalline silicon films, silicon oxide films, aluminum films, tungsten films and copper films.
In such a chemical mechanical polishing step, the object should be naturally achieved by conducting polishing only for a standard time of X/V (min) when an initial excess film of thickness X (Å), formed by embeding a wiring material in grooves or the like is polished at a removal rate of V (Å/min). In an actual production step of semiconductor devices, however, over polishing exceeding the standard time, X/V (min) is carried out for the purpose of removing the wiring material remaining on other portions than the grooves or the like. “Dishing” that a portion of wiring becomes a concave form or “erosion” that a portion of alternate wiring obtained by alternately forming a wiring portion and an insulating portion becomes a concave form is caused by such over polishing. These phenomena are not preferred in that yield of semiconductor devices is lowered.
Further, surface defects including so-called “scratches” of abrased-like state, may be caused by polishing in some cases. This phenomenon may also lower yield of semiconductor devices like the dishing and erosion in some cases.
Various compositions such as aqueous dispersions for chemical mechanical polishing for restraining such dishing and erosion, aqueous dispersions for chemical mechanical polishing for restraining the surface defects such as scratches and aqueous dispersions for chemical mechanical polishing having both properties in combination have heretofore been proposed.
For example, it is disclosed that excellent surface planarizing ability can be achieved by polishing a silicon wafer using a composition containing silica and piperazine (Japanese Patent Application Laid-Open No. 154760/1993). However, piperazine that is an essential component of this disclosed composition is an objective substance to regulate the amount of discharge to environment, and so the use thereof becomes a problem from the viewpoints of safety and influence on the environment.
In addition, compositions for polishing comprising at least one abrasive grain selected from silicon dioxide, aluminum oxide, cerium oxide, titanium oxide, silicon nitride, zirconium oxide and manganese dioxide and water, and additionally containing a basic organic compound in a state dissolved are disclosed. It is described that by these compositions for polishing, a great removal rate is achieved, and occurrence of surface defects on a polished surface can be lessened (see, for example, Japanese Patent Application Laid-Open No. 321569/1998).
With requirement of the increase of the degree of integration and the micronization in semiconductor devices, the micronization of a wiring pitch and the formation of a thinner dielectrics make progress. By the micronization of the wiring pitch, a silicon oxide film and a stopper layer composed of a nitride such as silicon nitride or titanium nitride are also made fine. When the stopper layer is over polished, however, the intended function of the stopper layer cannot be fulfilled, and erosion or the like are caused, so that the function as a semiconductor substrate may be impaired in some cases.
In addition, the surface defects including scratches on a polished surface have such influence that electrical properties of a dielectrics deposited thereon are deteriorated, and this influence becomes greater by the formation of a thinner dielectrics.
When a surface to be polished having the above-described stopper layer is polished with such a composition for polishing as described above, it is not easy to achieve both improvement of polishing and removal selectivity as to the layer to be polished and the stopper layer, and lessening of surface defects including scratches.
The term, “polishing and removal selectivity” as used herein means properties that a high rate of polishing and removal is achieved as to a material to be polished, while the rate of polishing and removal is low as to other materials, and means properties that when a surface to be polished composed of, for example, at least 2 material is polished, only one material to be polished can be polished with high efficiency without over polishing other materials to be polished. More specifically, the term, “polishing and removal selectivity as to a layer to be polished and a stopper layer” means properties that only the layer to be polished can be polished with high efficiency without over polishing the stopper layer when both layer to be polished and stopper layer are polished at the same time.
In order to solve the above-described problem, there have been proposed compositions improved in the polishing and removal selectivity as to a polysilicon film and a silicon oxide film and compositions controlled in removal rate (hereinafter also referred to as “polishing rate”) of polishing a nitride.
For example, Japanese Patent Application Laid-Open No. 321569/1998 discloses that the polishing rate of a silicon oxide film can be controlled by the above-described composition for polishing to increase the polishing and removal selectivity as to a polysilicon film and the silicon oxide film. However, it is not investigated to control the polishing rate of a nitride.
A composition for polishing comprising a tetramethylammonium salt, a base and hydrogen peroxide in combination is also disclosed. It is described that by this composition, the polishing rate of a nitride can be controlled to increase the polishing and removal selectivity as to both oxide and nitride (for example, Japanese Patent Application Laid-Open No. 270401/1998). However, this composition is excellent in the polishing and removal selectivity as to both oxide and nitride, but the polishing and removal selectivity as to polysilicon that becomes a material of a gate electrode and a nitride and the polishing and removal selectivity as to polysilicon and silicon oxide are not investigated.
With respect to the above-described composition for polishing, in particular, long-term stability in a high-concentration state that concentrations of respective components are higher than those in a polishing applicable state to be actually served for polishing is also not investigated, and the composition is assumed to be used within several hours after preparation of the composition. Therefore, this composition involves factors that cost is increased upon actual use, such as need of transporting and storing it in a state that the concentrations of the components has been controlled as low as those upon its use.